1. Field of the Invention
The present invention relates to the processes of assembling a flat-panel type image display apparatus and, more particularly, to a manufacturing method and apparatus for an image display apparatus in which upper and lower glass plates are seal-bonded using low-melting point glass.
2. Related Background Art
As an image display apparatus using an electron beam, for example, a flat-panel type image display apparatus has been developed. This image display apparatus comprises an electron-emitting device for generating an electron beam in a vacuum chamber sandwiched between a glass-face plate (substrate) and a glass-rear plate (substrate), and displays an image in such a manner that an electron beam emitted by the electron-emitting device is accelerated and irradiated onto a phosphor to emit light. Such electron-emitting device will be described below.
Conventionally, two types of electron-emitting devices, i.e., thermionic cathode devices and cold cathode devices, are known. The cold cathode devices include, for example, surface conduction type emitting devices, field emission type (to be referred to as "FE" type hereinafter), devices, metal/insulating layer/metal type (to be referred to as "MIM" type hereinafter) devices, and the like.
The surface conduction type electron-emitting device includes, for example, an element described in M.I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965), and another device to be described below.
The surface conduction type electron-emitting device utilizes a phenomenon in which electron emission occurs when a current flows in a direction parallel to the film surface of a small-area thin film formed on a substrate. As the surface conduction type electron-emitting device, in addition to an element using an SnO.sub.2 thin film by Elinson et al. described above, an element using an Au thin film G. Dittmer, "Thin Solid Films", 9, 317 (1972)!, an element using an In.sub.2 O.sub.3 /SnO.sub.2 thin film M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", 519 (1975), an element using a carbon thin film Hisashi Araki et al., "Vacuum", Vol. 26, No. 1, 22 (1983)!, and the like have been reported.
FIG. 46 is a plan view of the element by M. Hartwell et al., as an example of the typical element arrangement of such surface conduction type emission elements. Referring to FIG. 46, a conductive thin film 3004 consisting of a metal oxide is formed on a substrate 3001 by sputtering. The conductive thin film 3004 is formed into an H-shaped flat pattern. An electron emission portion 3005 is formed by performing an energization process called energization forming (to be described later) on the electro conductive thin film 3004. The interval L in FIG. 46 is set to fall within the range from 0.5 to 1 mm!, and the width W is set to be 0.1 mm!. Note that FIG. 46 illustrates the electron emission portion 3005 as a rectangular portion formed at the center of the conductive thin film 3004 for the sake of illustrative convenience, but it does not necessarily faithfully express the position or shape of the actual electron emission portion.
In the above-mentioned surface conduction type emission elements such as the element by M. Hartwell et al., it is a common practice to form the electron emission portion 3005 by performing an energization process called energization forming on the conductive thin film 3004 before electron emission. More specifically, in the energization forming, the electron emission portion 3005 is formed in an electrically high-resistance state in such a manner that the conductive thin film 3004 is locally destroyed, deformed, or denatured by applying a constant DC voltage or a DC voltage that increases at a very slow rate (e.g., about 1 V/min) across the two ends of the conductive thin film 3004. Note that a fissure is formed on a portion of the locally destroyed, deformed, or denatured conductive thin film. When an appropriate voltage is applied to the conductive thin film after the energization forming, electron emission occurs in the neighborhood of the fissure.
On the other hand, as the FE type elements, for example, an element by W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956), an element by C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5248 (1976), and the like are known.
FIG. 47 is a sectional view of the above-mentioned element by C. A. Spindt et al., as an example of the typical element arrangement of the FE type element. Referring to FIG. 47, an emitter wiring layer or interconnect 3011 consisting of a conductive material, an emitter cone 3012, an insulating layer 3013, and a gate electrode 3014 are formed on a substrate 3010. This element causes electron emission from the distal end portion of the emitter cone 3012 by applying an appropriate voltage across the emitter cone 3012 and the gate electrode 3014.
In another element arrangement of the FE type element, the emitter and the gate electrode are juxtaposed on the substrate to be substantially parallel to the substrate surface in place of the stacked structure shown in FIG. 47.
As an example of the MIM type element, an element by C. A. Mead, "Operation of Tunnel-emission Devices", J. Appl. Phys., 32, 646 (1961), or the like is known. FIG. 48 shows an example of the typical element arrangement of the MIM type element. FIG. 48 is a sectional view. Referring to FIG. 48, a metal lower electrode 3021, a thin insulating layer 3022 having a thickness of about 100 .ANG., and a metal upper electrode 3023 having a thickness of 80 to 300 .ANG. are formed on a substrate 3020. The MIM type element causes electron emission from the surface of the upper electrode 3023 upon application of an appropriate voltage across the upper and lower electrodes 3023 and 3021.
The above-mentioned cold cathode devices do not require any heaters since they can obtain electron emission at relatively low temperatures as compared to the thermionic cathode devices. Therefore, the cold cathode device has a simpler structure than the thermionic cathode device, and a very small element can be formed. Even when a large number of elements are arranged on a substrate at a high density, the problem of, e.g., heat melting of the substrate hardly occurs. The thermionic cathode device has a low response speed since it operates upon heating of a heater, while the cold cathode device has a high response speed.
For these reasons, extensive studies have been made to explore effective applications of the cold cathode device.
For example, since the surface conduction type electron-emitting device has the simplest structure and allows the easiest manufacture among the cold cathodes, a large number of elements can be formed over a large area. Hence, the method of driving an array of a large number of elements has been studied, as disclosed in Japanese Laid-Open Patent Application No. 64-31332 by the present applicant.
As for applications of the surface conduction type electron emitting device, for example, image forming apparatuses such as an image display apparatus, an image recording apparatus, and the like, a charged beam source, and the like have been studied.
In particular, as an application to the image display apparatus, as disclosed in U.S. Pat. No. 5,066,883 and Japanese Laid-Open Patent Application No. 2-257551 and No. 4-28137 by the present applicant, an image display apparatus which uses a combination of the surface conduction type electron-emitting device and a phosphor that emits light upon irradiation of an electron beam has been studied. The image display apparatus which uses a combination of the surface conduction type emission element and the phosphor is expected to have higher characteristics than conventional image display apparatuses. For example, the image display apparatus of this type is superior to liquid crystal display apparatuses that have become popular in recent years, since it is of emissive type and requires no backlight, and has a wide field angle.
The method of driving an array of a large number of FE type elements is disclosed in, e.g., U.S. Pat. No. No. 4,904,895 by the present applicant. As an example of an application of the FE type element to an image display apparatus, a flat-panel type display apparatus reported by R. Meyer et at. is known R. Meyer, "Recent Development on Microtips Display at LETI", Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)!.
Also, an example of application of an array of a large number of MIM type elements to an image display apparatus is disclosed in, e.g., Japanese Laid-Open Patent Application No. 3-55738 by the present applicant.
Of the above-mentioned image display apparatuses using the electron-emitting devices, the flat-panel type display apparatus has been receiving a lot of attention as an alternative to a CRT type display apparatus since it can attain a small-space, lightweight structure.
An image display apparatus with the above-mentioned electron-emitting device will be described below. FIG. 49 is an exploded view showing the arrangement of an image display apparatus. FIGS. 50A and 50B are respectively a perspective view and a side view showing the assembled state of the image display apparatus shown in FIG. 49.
Referring to FIG. 49, the image display apparatus is constituted by a glass-face plate 271 having red, blue, and green light-emitting members 271c for displaying an image, which are formed on a surface opposing an electron-emitting device 273c, a glass-rear plate 273 formed with the electron-emitting device 273c, and an outer frame 272 which is manufactured by, e.g., boring glass to constitute a vacuum chamber to be sandwiched between the glass-face plate 271 and the glass-rear plate 273. In order to prevent the vacuum chamber from being destroyed by atmospheric pressure acting on the vacuum chamber, a spacer 74 shown in FIG. 50B is arranged, as needed.
Alignment marks 271a and 271b used for adjusting the positional relationship between the light-emitting members 271c and the electron-emitting device 273c are formed on the glass-face plate 271, and alignment marks 273a and 273b are similarly formed on the glass-rear plate 273. Note that these alignment marks are formed at positions where they do not interfere with the light-emitting members 271c and the electron-emitting device 273c.
Fusion-bonding surfaces 272a and 272b of the outer frame 272, which respectively contact the glass-face plate 271 and the glass-rear plate 272, are coated with low-melting point glass in advance, and are pre-baked. The glass-face plate 271, the outer frame 272, and the glass-rear plate 273 are manufactured using soda-lime glass consisting of the same material having the same coeffcient of thermal expansion.
In this arrangement, as shown in FIGS. 50A and 50B, the glass-face plate 271 and the glass-rear plate 273 are respectively fusion-bonded to the outer frame 272 by the low-melting point glass applied to the two surfaces of the outer frame 272, thus forming a closed chamber. At this time, the plates 271 and 273 are arranged, so that the alignment mark 271a of the glass-face plate 271 and the alignment mark 273a of the glass-rear plate 273, and the alignment mark 271b of the glass-face plate 271 and the alignment mark 273b of the glass-rear plate 273 respectively have predetermined positional relationships therebetween, thereby accurately determining the positional relationship between the light-emitting members 271c and the electron-emitting device 273c. Such alignment process can prevent color misregistration and luminance variations of characters, images, and the like. Note that the low-melting point glass is in the solid state at normal temperature (room temperature), and is in the molten state at a temperature of 400.degree. C. or higher. Therefore, in order to fusion-bond the glass plates using the low-melting point glass, the temperature cycle including the heating and cooling processes is required.
As a conventional manufacturing method of an image display apparatus assembled by aligning the positions of a plurality of plates, a method proposed by Japanese Laid-Open Patent Application No. 59-94343, a method proposed by Japanese Laid-Open Patent Application No. 58-214245, or the like is known. These references disclose, e.g., a method of aligning the positions of a plurality of plates that constitute a flat-panel type image display apparatus using holes and alignment pins formed on the plates. However, in the method of performing position alignment using the alignment pins, the alignment accuracy may deteriorate depending on the accuracy of the holes and alignment pins formed on the plates.
On the other hand, a method of aligning the positions of a rear plate formed with an electron-emitting device and a face plate serving as a display surface by matching alignment marks formed outside the image display effective area while observing these marks using, e.g., a microscope is known. However, in the method of performing position alignment using alignment marks, when the positions of the plates are aligned to each other using, e.g., a microscope at room temperature, and thereafter, the plates are heated up to 400.degree. to 450.degree. C. to seal-bond (adhere) these plates using low-melting point frit glass, the plates may be displaced from each other due to their thermal expansion.
On the other hand, since the support points for the plates of upper and lower heating plates for heating the face plate and the rear plate do not always match each other, a shearing force acts among the face plate, outer frame, and rear plate due to shrinkage of the upper and lower heating plates in the cooling process after the rear plate is fixed to the face plate, resulting in peeling at the bonded portion. Similarly, in the process of fixing a spacer to the face plate or rear plate as well, a shearing force acts between the plate and spacer during cooling, and peeling at the bonded portion or destruction of the spacer due to low mechanical strength of the spacer may occur.